Tropical
Highlights - October 2017

Sea surface
temperatures (SSTs) during October 2017 were below-average across most of the central and eastern equatorial
Pacific (Fig. T18,
Table T2). The latest monthly
Niņo indices were -0.1°C for the Niņo 4
region, -0.5°C
for the Niņo 3.4 region, and -1.3°C for the Niņo 1+2 region (Table
T2, Fig. T5). The depth of the oceanic thermocline
(measured by the depth of the 20°C isotherm) was below-average over much of the
eastern equatorial Pacific (Figs. T15, T16), and
the corresponding sub-surface temperatures were 1-4°C below average (Fig. T17).

Also during October, the lower-level
trade winds were near-average across the equatorial Pacific while the
upper-level westerly winds were above-average over much of the central and
eastern equatorial Pacific (Table T1, Figs. T20, T21). Meanwhile, convection was enhanced over the
Maritime Continent and suppressed over the central equatorial Pacific (Figs. T25, E3). The latest Tahiti minus Darwin Southern
Oscillation Index (SOI) was +0.9 (Table T1). Collectively, these oceanic and atmospheric
anomalies reflect the onset of La Niņa conditions.

For the latest status of the ENSO
cycle see the ENSO Diagnostic Discussion at:
http://www.cpc.ncep.noaa.gov/products/analysis_monitoring/enso_advisory/index.html